Telephone answering machines generally require two magnetic tapes. Upon activation by an incoming call, an announcement, recorded on a first tape (T-1), is transmitted over the telephone line to the calling party. A second tape (T-2) is activated after the announcement has been completed and is used for recording and storing incoming messages. Announcement tape (T-1) is typically an "endless" tape that stores one or more pre-recorded announcements. In an effort to minimize cost and space, many answering machine manufacturers have eliminated the announcement tape in its entirety and now use a single tape to deliver an outgoing announcement and to record incoming messages. The single magnetic tape is partitioned to store announcements in one region, message address data in another, and incoming messages in yet another region. During operation, however, the tape must move from one region to another in order to deliver the announcement and then position itself to record the incoming message. Even with fast-forward capability it frequently takes an undesirable amount of time to move from one region of the tape to another.
Use or a solid state storage apparatus to deliver the outgoing announcement has, for the most part, solved the time delay problem. The solid state storage apparatus is preferably a Random Access Memory (RAM) that stores a large number of binary digits. These digits are extracted from the RAM in a predetermined sequence and converted into a time varying electrical signal which comprises the outgoing announcement formerly stored on announcement tape (T-1). The technique of storing and delivering pre-recorded announcements using solid state storage apparatus is sometimes referred to as "voice synthesis." While this technique is useful, it is not without problems. In the event or a power outage, loss of information stored in the RAM is possible unless a more "nonvolatile" device, such as an EPROM, is used. Alternatively, battery backup may be provided to safeguard the stored information; but batteries have a limited life, increase the cost and size of the telephone answering machine, and impose the burden of purchasing and installing batteries.
Additionally, the quality of speech available using solid state storage apparatus is proportional to the number or binary digits used to encode the speech. High quality speech, therefore, requires a large memory space--much of which is wasted to assure that a sufficient amount will be available for the longest outgoing announcement.
It is therefore an object of the present invention to provide a telephone answering machine with solid state storage apparatus to deliver outgoing announcements and thereby minimize the time delay between the end of the announcement and the time when a caller can enter his/her message.
It is another object of the invention to safeguard the information stored in the solid state storage apparatus during a power failure in a cost effective manner, and without the disadvantages associated with a battery.
It is yet another object of the invention to provide optimum speech quality for announcements of different length.